STAINLESS STEEL BONDED SEALING WASHERS WITH GREY EPDM

Bonded Sealing Washers with Grey EPDM — A bonded sealing washer is a composite component rather than a single-material washer - a metal ring bonded permanently to an EPDM rubber seal - built specifically to close off the fixing point against water or gas ingress in addition to doing the usual job of spreading the fastener's clamping load. As the bolt or screw is tightened, the EPDM ring compresses against the panel surface around the fixing hole, closing the small gap that would otherwise exist around the fastener shank and giving a genuinely watertight seal rather than just a mechanical bearing surface. EPDM is chosen specifically for its resistance to weathering, ozone, and a wide range of chemicals, which is why these washers are the standard choice under roofing sheet fixings, external cladding, enclosures, and any panel fixing where keeping water and air out at the fastener is as important as holding the panel down. It is worth being clear that the seal is largely a one-time event: once the EPDM has been compressed and set against a surface, it may not recover fully if the fastener is removed and refitted, so for anything where weatherproofing genuinely matters - a roof, an outdoor enclosure - fitting a fresh sealing washer on reassembly is the safer practice rather than reusing the old one. Getting the metal washer's finish right relative to the panel material also matters here in a way it does not for a plain flat washer, since a mismatched combination - an incompatible metal washer against a dissimilar panel material - can set up galvanic corrosion at exactly the point the seal is trying to protect. A2 (304-equivalent) stainless is the standard metal for most roofing and cladding applications, giving good general corrosion resistance without excessive cost, while A4 (316-equivalent) is worth the upgrade specifically for coastal roofing, marine-adjacent cladding, or heavily salted environments, where A2 would otherwise be the first thing to show corrosion. To choose correctly, match the metal washer bore to the fastener diameter, confirm the EPDM disc diameter suits the fixing hole in the panel, and check the metal finish is compatible with the panel material.

FAQs
Can bonded sealing washers be used on both metal and timber cladding?
Yes, they are commonly used on both, provided the fixing hole and fastener are matched correctly; the EPDM disc does the sealing regardless of the substrate beneath it.

Are bonded sealing washers reusable?
Once compressed and set, the EPDM seal may not recover fully if removed and refitted, so for critical weatherproofing applications, fitting a new sealing washer on reassembly is generally recommended.

How do I choose the correct bonded sealing washer?
Match the metal washer bore to the fastener diameter, confirm the EPDM disc diameter suits the fixing hole in the panel, and check the metal washer's finish is compatible with the panel material to avoid galvanic corrosion.